COVER CROPS in South African Vineyards

CHAPTER 7 EFFECT OF COVER CROPS ON SOIL CARBON AND MINERALS

Nitrogen in the soil Nitrogen was applied at 14 kilogram per hectare during the second week of April, when cover crops were sown, and at 14 kilogram per hectare when they reached the two-to-four-leaf stage. Soil nitrogen levels were measured in the work row at grapevine full bloom (early November) and again after harvest (early March). Figure 7.7 shows the soil nitrogen levels at grapevine full bloom. Two management strategies were applied. Where weed control was started in August, all cover crops were sown annually.Where weed control was started later, no cover crops were sown in 1995 and 1997, and no legumes were sown in 1999, to test whether cover crops could reseed themselves. er

14,00

12,00

10,00

Henog rye Overberg oats Saia black oats Grazing vetch Faba beans

8,00

6,00

Paraggio bur medic Kelson snail medic Woogenellup clover No cover crop

4,00

2,00

Nitrogen in milligram per kilogram soil

0,00

1996 Season 4

2002 Season 10

1996 Season 4

2002 Season 10

Weed control August

Weed control October-November

FIGURE 7.7. Soil nitrogen measured at grapevine full bloom in the 0–300-millimetre soil layer in cover-crop treatments compared to a control in the Coastal region. Adapted from Fourie et al (2007). In general, cover crops were not able to re-establish, and dry-matter production in the latter treatment was lower than in the treatment where cover crops were sown annually. This is discussed in more detail in Coastal Region in Chapter 4 (p79). Overall nitrogen levels in the soil were higher by the fourth year for the treatments where legumes were sown annually than for either the grass treatments or those where legumes had not been sown the previous year.

132